1. Field of the Invention
The present invention relates to a method and apparatus for detecting surging in an internal combustion engine.
2. Description of the Related Art
As measures taken against exhaust gas pollution and fuel consumption, a lean burn system has recently been developed. According to this lean burn system, a lean mixture sensor is provided for generating an analog current proportional to the lean air-fuel mixture in an exhaust pipe of an engine. Feedback control of the air-fuel ratio of the engine is possible using the analog output of the lean mixture sensor, thereby attaining an arbitrary air-fuel ratio on the lean side.
In such a lean burn system, the controlled air-fuel ratio is brought close to a misfiring limit to reduce the NOx emission. If the characteristics of the lean mixture sensor fluctuate, the engine may suffer from surging or misfiring, thus reducing drivability.
In the prior art, the detection of surging or misfiring is carried out by using a gravity sensor. Such a sensor, however, is disadvantageous in cost.